Design of an ultracompact low-power all-optical modulator by means of dispersion engineered slow light regime in a photonic crystal Mach-Zehnder interferometer

We present the design procedure for an ultracompact low-power all-optical modulator based on a dispersion-engineered slow-light regime in a photonic crystal Mach-Zehnder interferometer (PhC MZI), selectively infiltrated by nonlinear optical fluids. The dispersionless slow-light regime enhancing the nonlinearities enabled a 22 μm long PhC MZI to operate as a modulator with an input power as low as 3 mW/μm. Simulations reveal that the switching threshold can be controlled by varying the optofluidic infiltration.     

EIT-based MZ-MMI all-optical switch

We propose a new control structure for all-optical switching in multimode inference (MMI)-based Mach–Zehnder interferometer (MZI) devices. This structure is composed of an MZI doped by three-level nanocrystals for the realization of electromagnetically induced transparency (EIT) in the lower arm. We use two different intensities of control field for two states of the proposed switch. Using a control field in both of the two switching states is necessary, where the EIT region is transparent. By changing the intensity of the control field, the refractive index of the doped region changes, which makes the phase difference between the two arms of the MZI. Hence, the switching operation takes place. Simulation results show that the extinction ratio of the device is ?32dB in the worst case.     

Ultrafast low-threshold all-optical switch implemented by arrays of ring resonators coupled to a Mach-Zehnder interferometer arm: based on 2D photonic crystals

Using an array of m x n nonlinear ring resonators (m = 1, 3, 5, and n = 1, 2, 3) coupled to the upper arm of a Mach-Zehnder interferometer (MZI), we have proposed an all-optical switch structure. Using a 5 x 3 array, we have shown the possibility of designing an all-optical switching device with a threshold intensity as low as 15 mW/m(2) and switching window of approximately 35 ps. While using m x 1 arrays, we have achieved switching windows smaller than 10 ps, at the expense of higher switching thresholds, ranging from 37 to 55 mW/m(2). The whole structure is based on a square lattice photonic crystal of lattice constant a = 600 nm, formed by rods of radius r = 90 nm in an air background. The linear rods' refractive index is taken to be the same as that of Si(0.75)Ge(0.25); i.e., n(r) = 3.6, whereas the nonlinear rod's refractive index and Kerr index parameter are taken to be n(0) = 1.4 and n(2) = 10(-14) m(2)/W. The center wavelength at which the nonlinear rings are designed to make the resonance is taken to be lambda(0) = 1550 nm in free space.     

Filters based on spoof surface plasmon polaritons composed of planar Mach–Zehnder interferometer

Abstract

Filter characteristics of a planar Mach–Zehnder interferometer (MZI) structure composed of periodically thin corrugated metal films were studied here. From theoretical simulation, spoof surface plasmon polaritons can propagate along the periodically thin corrugated metal films in microwave frequency, which can be excited by a coplanar waveguide. When the two arms of the MZI have the same length with the angle between them being 60°, the MZI structure has a very wide bandwidth with 8.6 GHz. By changing the length of one of the interference arms, a novel low-pass filter based on the planar MZI structure with two notched frequencies was proposed. The proposed planar structure can find potential applications in developing surface wave devices in integrated microwave circuits and systems.     

Ultrahigh speed all-optical AND logic gate using integrated silicon-based MZI device

In this paper, we present a device with a silicon-on-insulator (SOI) based symmetrical Mach–Zehnder interferometer (MZI) structure to perform the ultrahigh speed all-optical AND logic gate function. Simulation results show that, while the operation speed is at a bit rate of 200 Gbit s^?1, the output parameters including extinction ratio and eye-opening ratio for outcome AND logic gate signal can, respectively, reach as high as ～12.8 dB, and ～0.94 in the case of a 5 mm long SOI waveguide by means of judiciously adjusting the initial conditions, such as incident signal and probe continuous-wave (CW) powers.     

High sensitivity liquid surface deformation sensor based on cascaded Bowknot Type Tapers

A liquid surface deformation sensor with high sensitivity based on a Mach–Zehnder interferometer (MZI) was demonstrated. The MZI was constructed by cascading two Bowknot Type Tapers (BTTs) with an interval of 1.0?cm. As the liquid surface changes gradually from the position higher than the optical fibre to a position lower than the optical fibre, the external environment of the optical fibre changes gradually from the liquid to air, this will result in a change of the interference of the MZI. By measuring the intensity variations of the resonant wavelength, the liquid surface deformation in the range from 0 to 5.22?mm can be determined with a high sensitivity of 0.99?dB/mm.     

3D characterization of microstructured poly(methacrylic acid) thin films via Mach-Zehnder interference microscopy

We demonstrate the adaption of a further developed Mach-Zehnder interference (MZI) microscope for the rapid 3D characterization of transparent microstructured polymer thin films. In order to quantify the accuracy of the Mach-Zehnder interferometer, comparative film thickness measurements of photolithographically patterned poly(methacrylic acid) polymer brushes are performed employing two alternative techniques: white light profilometry (WIM) and atomic force microscopy (AFM). When the refractive index of the polymer brushes is calculated from MZI data, we obtain a good agreement with results received from an independent method (ellipsometry).In contrast to surface probing techniques such as AFM or WIM, Mach-Zehnder interferometry is a transmitted light method that measures both surface height profiles and refractive index distributions. MZI thus enables the quantification of film homogeneity with respect to height and density variations at the lateral resolution of a refraction limited microscope. We conclude that MZI is an adequate tool for the rapid and non-destructive characterization of structured polymer thin films. This method should be particularly useful for production quality control of microstructured polymer thin films which possess great potential in electronic device fabrication and biotechnology.     

Ultrasensitive liquid refractometer based on a Mach-Zehnder micro-cavity in optical fibre fabricated by femtosecond laser-induced water breakdown

Abstract

A Mach–Zehnder (MZ) micro-cavity with two symmetric openings in single mode fibre (SMF) was fabricated by femtosecond laser-induced water breakdown. The micro-cavity is rightly across half of the fibre core, and the opening size of the micro-cavity is 10 μm × 100 μm. The micro-cavity and the remaining half of the fibre core constitute two arms of the Mach–Zehnder interferometer (MZI). The MZI with micro-cavity immerged in water shows perfect interference spectrum due to the regular shape and smooth internal surface of the micro-cavity. The insertion loss is only –8 dB and the contrast of one MZI peak reaches more than 40 dB. The MZI with micro-cavity in SMF can be used as an ultrasensitive liquid refractometer as its ultrahigh refractive index (RI) sensitivity (14296.98 nm/RIU), high RI resolution (1 × 10^?5 RIU), good linearity (99.62%) and low temperature crosstalk (0.04 nm/°C).     

Highly sensitive optical length measurement by using a microwave photonic filter with multi-passband

In this paper, a method for optical length measurement that employs a multi-passband microwave photonic filter (MPF) is analysed and demonstrated experimentally. The MPF consists of a sliced broadband light source, a phase modulator, a dual-parallel dispersion medium and a photodetector (PD). By cascading two Mach–Zehnder interferometers (MZIs) with different arm length difference, the MPF with eight passbands has been obtained. The variation of the length difference of MZI will lead the change of the free spectral range (FSR) of the interference spectrum, as well as the frequency of the passbands. By changing the arm length of the MZI, a high length measuring sensitivity of ?2.420?GHz/mm has been achieved. The MPF has broad application prospects in the field of multi-parameter sensing. Moreover, the sensor reveals the advantages of highly sensitive, easy to implement and is able to overcome the influence of the environmental perturbation, for example temperature.     

Theoretical investigation of phase-based all-optical logic gates based on AlGaAs microring resonators

We propose and numerically verify a phase-based all-optical logic gates (AND, OR, XOR, NOT, NAND, NOR and XNOR, i.e. all seven basic logic gates) operation scheme based on cascaded AlGaAs microring resonators. The logic function realization is supported by the signal light phase change and extraction, the phase control in this scheme depending on cross phase modulation (XPM) in the AlGaAs microring. By inputting a non-return zero (NRZ) intensity signal as pump light, the probe light (continuous-wave, CW) will experience different phase shift and then a phase-based logical function can be obtained in this process. By choosing different pump power level, reference phase and the output port of a Mach–Zehnder interferometer (MZI), all seven basic logic operations can be realized by using the same device. The modulation depth, bandwidth and minimum power requirement of this scheme have also been discussed in detail.     

All-optical arithmetic unit with the help of terahertz-optical-asymmetric-demultiplexer-based tree architecture

An all-optical arithmetic unit with the help of terahertz-optical-asymmetric-demultiplexer (TOAD)-based tree architecture is proposed. We describe the all-optical arithmetic unit by using a set of all-optical multiplexer, all-optical full-adder, and optical switch. The all-optical arithmetic unit can be used to perform a fast central processor unit using optical hardware components. We have tried to exploit the advantages of both optical tree architecture and TOAD-based switch to design an integrated all-optical circuit that can perform binary addition, addition with carry, subtract with borrow, subtract (2's complement), double, increment, decrement, and transfer operations.     

Wind-velocity lidar measurements by use of a Mach-Zehnder interferometer, comparison with a Fabry-Perot interferometer

We present the first wind-velocity profiles obtained with a direct-detection Doppler lidar that uses a Mach-Zehnder interferometer (MZI) as spectral discriminator. The measurements were performed in the lower stratosphere, between 10 and 40 km in altitude, at the Observatoire de Haute Provence (OHP), France, during nighttime. They are in excellent agreement with those obtained simultaneously and independently with the already validated double Fabry-Perot interferometer (FPI) of the OHP Doppler lidar (mean difference lower than the combined standard deviation). A statistical analysis shows that the random error obtained with this experimental MZI is 1.94 times the Cramer-Rao lower bound and is approximately half of that given by the FPI (both operating in photometric mode). Nevertheless, the present MZI measurements are sensitive to the presence of atmospheric particles and need an additional correction, whereas the OHP FPI is designed to be insensitive to particulate scattering.     

Design and numerical simulation of an optofluidic pressure sensor

We present a numerical design procedure for an all-optical compact sensor by means of integrating the optofluidic switch polymer interferometers to measure the microfluidic air pressure and flow rate. The design is based on a flexible air gap optical cavity that can generate an interference pattern when illuminated by a monochromatic light. The optical interference pattern directly depends on the pressure. In our numerical simulations, we take the effects of fluid flow rate, solid deformation, and the light interference into account. We use the beam propagation method for simulating the optics and the finite element method for simulating the mechanics. The significance of the proposed sensor lies with its low power consumption, compactness, low cost, and short length. This sensor can operate under pressure range of 0-60±6% Pa at a constant temperature of 20 °C.     

Theoretical and experimental studies of polarization mode dispersion of an electro-optic Mach-Zehnder modulator

A theoretical model is developed to study the polarization mode dispersion effect in an electro-optic Mach-Zehnder interferometric (MZI) modulator. The Stokes parameters and differential group delay (DGD) of the output light of a MZI modulator can be analytically derived with the proposed model, which is based on a three-dimensional Maxwell's wave equation approach. The theoretical model is validated to the extent possible by comparing the theoretical results of the Stokes parameters and DGD with experimental measurements that are based on the wavelength-scanning method and the Jones matrix eigenanalysis method.     

Very-high-speed all-optical code-division multiplexing systems using a 2n prime code

We demonstrate experimental all-optical code-division multiplexing (AO-CDM) systems using 64-ps optical pulses and a 2" prime code of n = 3. A distinguishing feature of this experiment is that the modulation of an ultrashort optical clock stream by electrical data is realized without using any optical intensity modulator at each transmitter. Moreover, only low-cost optical 2 x 2 couplers and fiber delay lines are employed to implement all-serial encoders and decoders for a 2n prime code.     

L-Band multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror and dual-channel Mach–Zehnder interferometer

In this letter, we propose and demonstrate an L-Band linear cavity tunable multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror (NOLM) and dual-channel Mach–Zehnder interferometer (MZI) . The NOLM provides the intensity-dependent transmissivity, can effectively alleviate the mode competition and beating caused by the homogeneous gain broadening, so that the multi-wavelength lasing can be achieved at room temperature. The dual-channel MZI, configured by linking the two outputs of the single-channel MZI, serves as comb filter. By adjusting the polarization controller in NOLM and pump power, the tunable multi-wavelength output at 1600 nm can be achieved. Moreover, the output stability of the laser has also been accomplished .     

Effect of beam waists on performance of the tunable fiber laser based on in-line two-taper Mach-Zehnder interferometer filter

A tunable fiber ring laser based on an in-line two-taper Mach-Zehnder interferometer (MZI) filter was realized, and the effect of beam waists of the tapers on performance of the laser was investigated with different beam waists of 70 μm, 49 μm, and 33 μm. Experimental results show that the tunable laser with MZI length of 1 m and beam waist of 49 μm can cover 16.1 nm with tuning steps of 0.07-0.5 nm, a bandwidth of 10 pm, and a side mode suppression ratio (SMSR) of 40-50 dB. Tuning range is not only determined by the number of the cladding modes but is also affected by the filter loss. Tuning step is determined by the differences of the effective refractive indexes between the cladding modes and the core mode. SMSR is determined by the balance between the extinction ratio of the filter and the cavity loss of the laser due to MZI filter.     

All-optical switch using optically controlled two mode interference coupler

In this paper, we have introduced optically controlled two-mode interference (OTMI) coupler having silicon core and GaAsInP cladding as an all-optical switch. By taking advantage of refractive index modulation by launching optical pulse into cladding region of TMI waveguide, we have shown optically controlled switching operation. We have studied optical pulse-controlled coupling characteristics of the proposed device by using a simple mathematical model on the basis of sinusoidal modes. The device length is less than that of previous work. It is also seen that the cross talk of the OTMI switch is not significantly increased with fabrication tolerances (±δw) in comparison with previous work.     

Highly sensitive refractive index sensor based on two cascaded special long-period fiber gratings with rotary refractive index modulation

We present a refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer (MZI) formed by two cascaded special long-period fiber gratings (LPFGs) with rotary refractive index modulation (RLPFGs), in which the coupling occurred between the guided mode and the high-order asymmetric cladding mode. The experimental results show that the RI sensitivity of a refractometer with an interaction length of 40?mm is up to 58.8?nm/RI in the range of 1.3344 to 1.3637, which is 3.5 times higher than that of an MZI formed by two normal LPFGs. The temperature sensitivity for the same parameters of an RLPFG-MZI is about 0.03?nm/°C. Such a kind of high-sensitivity, easy-to-fabricate and simple-structure interferometer may find applications in the chemical or biochemical sensing fields.     

High sensitivity of taper-based Mach-Zehnder interferometer embedded in a thinned optical fiber for refractive index sensing

A taper-based Mach-Zehnder interferometer (MZI) embedded in a thinned optical fiber is demonstrated as a highly sensitive refractive index (RI) sensor. A RI sensitivity of 2210.84 nm/RIU (refractive index unit) is obtained at the external RI of 1.40, which is ten times higher than that of normal taper- and long-period fiber grating (LPFG)-based sensors. The sensitivity can be further improved by decreasing the diameter of the thinned fiber and increasing the interferometer length of the MZI. The proposed MZIs have lower temperature sensitivities compared with normal fiber sensors, which is a desirable merit for RI sensors to reduce the cross sensitivity caused by thermal drift.